This invention relates generally to fluid delivery systems and, more particularly, to an interface for pressure transfer to a pressure sensor.
In many fluid delivery systems, it is desirable to monitor the pressure in tubing functioning to deliver a fluid to a subject. Fluid line pressure may be monitored for a number of reasons. In various medical and industrial applications, it may be important to deliver precise amounts of fluid at predetermined rates. In such cases, fluid line pressure may be monitored to assure that the precise volumes of fluids are delivered at the appropriate rates. Likewise, it may be important to the consistency of a process that fluid be delivered at a specific pressure. Similarly, it may be important to maintain the pressure within a specific range for safety reasons.
Where a specific fluid line pressure is expected but the actual pressure varies from the expected value, an occlusion or other problem may be present in the line. By monitoring fluid line pressure and observing unexpected pressure variances, the operator can take the necessary steps to remove the occlusion or remedy the other problem or problems present in the fluid line.
Traditional fluid delivery systems take pressure measurements directly from conventional cylindrical tubing used to conduct the parenteral fluid to the patient. Because of the manufacturing variances in making such tubing and the possibility of deformation of the tubing over use resulting in a change in its shape, there is generally a less than optimal interface between fluid line pressure and the sensing element. A poor interface can result in reduced accuracy of the pressure readings.
Additionally, the positioning of the pressure sensor in the infusion pump during manufacture can vary due to standard manufacturing procedures and tolerances. This variance in sensor position in the instrument can also contribute to reduced accuracy because the tubing may not be optimally positioned in relation to the sensor when in use. It would be desirable to provide a system which compensates for such manufacturing tolerances to achieve an optimum interface.
A further consideration is the uniformity in interface characteristics across the sensor when the conduit is installed. Specifically, in traditional fluid delivery systems, the shape of the pressure transferring element often produces a non-uniform stress distribution across itself upon coupling with a pressure sensor, thereby reducing the accuracy of the pressure information transferred.
Moreover, such traditional systems often lack a pre-load feature where the conduit is loaded against the pressure sensor with sufficient force so that the full range of possible negative pressures that may be experienced in the conduit can be sensed. Such a pre-load can apply increased stress on the pressure transferring element and may reduce the uniformity of stress across the element. Optimizing the interface for such pre-load conditions is also desirable.
Another system used for transferring pressure to a sensor is a diaphragm contained on a rigid component that is incorporated into conventional tubing. Pressure levels in an infusion conduit can reach relatively high levels and the diaphragm must be formed so that such pressures do not cause it to rupture. When placed in contact with a pressure sensor, the sensor provides support for the diaphragm thus decreasing the chances of rupturing. However, cases may occur where the diaphragm is in the unloaded or "free" state in which it is not in contact with the sensor. The diaphragm is subject to increased risk of rupture when subjected to large internal pressures.
Increasing the thickness or stiffness of the diaphragm may reduce the possibility of rupture in the free configuration but may also reduce its sensitivity to internal pressures, thus decreasing the accuracy of pressure readings. It would be desirable to increase the resistance of a diaphragm to rupture while not lowering its interface characteristics with the sensor so that accurate pressure readings may be taken.
Accordingly, there remains a need for a segment, to be used, in a fluid delivery system that has a pressure transferring element with a shape optimized for uniformly distributing pressure created stress across its face, an optimal interface with a sensing element, and an optimal pre-load displacement upon coupling with a sensing element. There also is a need for a pressure transferring element that is capable of receiving the relatively high internal pressures without rupture or bulge while at the same time, able to transfer internal pressures to the sensor accurately. The present invention fulfills those needs.